Intravenous fluid control systems are well-known in the prior art. The most primative devices are simply clamps, inserted in physical contact with the fluid line, which are manually adjusted to accomplished the desired flow rate. The invention described in my U.S. Pat. No. 4,137,915 utilizes an electro-mechanical system including an electrically operated clamp, a switch in series with the clamp, and a motor-driven screw and spring arrangement to permit the reservoir to decrease in weight at a rate dependent on the motor speed. Such a system, though a significant advance in the art, requires many moving parts and is limited in accuracy by sensitivity of the switch and mechanical friction and hysteresis.